Project Summary/Abstract Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in reproductive-aged women worldwide. In addition to infertility, many women with PCOS have metabolic abnormalities that result in an increased risk of type 2 diabetes and cardiovascular disease. Studies have shown that the large intestine contains a complex community of microorganisms (the gut microbiome), that the gut microbiome is altered in humans with metabolic disorders such as obesity and type 2 diabetes, and that changes in the gut microbiome may contribute to metabolic dysregulation. Several recent studies, including two from our lab, reported that changes in the gut microbiome were associated with PCOS in women and in rodent models. We also showed that these changes correlated with hyperandrogenism in women with PCOS and in the letrozole-induced PCOS mouse model, suggesting that elevated androgens may regulate the gut microbiome in females. Our preliminary studies showed that fecal microbiome transplantation from letrozole-treated mice increased the weight of germ-free mice and that co-housing letrozole-treated mice with placebo mice resulted in improvement of the PCOS metabolic phenotype. Our results support the idea that there is a direct link between the gut microbiome and PCOS and also suggest that manipulation of the gut microbiome may improve PCOS symptoms. Studies also showed higher serum LBP in women with PCOS and in PCOS mouse models, suggesting that gut permeability may be altered in PCOS. Collectively, these studies suggest that a microbial imbalance, or ?dysbiosis?, in the gut linked to hyperandrogenism may contribute to the development and pathology of PCOS. We propose to use the letrozole-induced PCOS mouse model to test the hypothesis that androgen action via the androgen receptor results in dysregulation of the gut microbiome and gut epithelial function, which in turns contributes to the development and pathology of PCOS. In Aim 1, we propose to use the androgen receptor antagonist, flutamide to determine if the androgen receptor is necessary for changes in the gut microbiome, gut permeability and the metabolic phenotype. In Aim 2, we will use germ- free mice to determine whether the gut microbiome is necessary and sufficient for development of a metabolic phenotype. Finally, in Aim 3, we will use fecal microbiome transplantation to ascertain whether modulation of the gut microbiome can improve PCOS reproductive or metabolic phenotypes. In addition, we will use metagenomics coupled with metabolomics to identify which microbes and metabolites are altered in the letrozole-induced PCOS mouse model in order to identify potential therapeutic targets. Results from this proposal have the potential to answer fundamental questions concerning the role of the gut microbiome in the development and pathology of PCOS and expedite development of novel treatment options for women with PCOS (e.g., bioactive molecules, pre- or probiotic therapies).